Condition sensing assembly positioned as washer

ABSTRACT

A sensing element mounted like a washer having an outer fiber layer bonded to and insulating the flat, circular top surface of an upper metal sheet, which, in cross section, is hook shaped on opposite, outer sides. The other side of the upper metal surface is insulated by a bottom fiber layer. A circular Belville spring washer contacts the bottom fiber layer on one side and a circular metal support structure on the other side. In cross section the support structure has an elongated vertical part extending from the shaft location outward, terminated by a flange which extends further under and to the end of the spring. The hook shaped part ends in the area under the flange. A point on the upper sheet is jointed to a tab to which an electrical lead is soldered. The bottom of the support is sweat soldered to a thin, circular metal sheet, the end of which at one point is jointed to a tab which extends past the top sheet and to which a second electrical lead is soldered. Upon loosening of a nut or bolt with which the invention is used, the spring forces the upper and lower elements apart until the hook shaped part contacts the flange of the support, thereby completing an electrical circuit between the two leads which signals the loose condition.

Unite States Patent [191 Rumbaugh 51 May 29, 1973 Don K. Rumhaugh, 1668 Los Altos Road, San Diego, Calif. 92109 [22] Filed: Sept. 14, 1971 [21] Appl. No.: 180,284

[76] Inventor:

Primary Examiner-R0bert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-Schel1in and Hoffman [57] ABSTRACT A sensing element mounted like a washer having an outer fiber layer bonded to and insulating the flat, circular top surface of an upper metal sheet, which, in cross section, is hook shaped on opposite, outer sides. The other side of the upper metal surface is insulated by a bottom fiber layer. A circular Belville spring washer contacts the bottom fiber layer on one side and a circular metal support structure on the other side. In cross section the support structure has an elongated vertical part extending from the shaft location outward, terminated by a flange which extends further under and to the end of the spring. The hook shaped part ends in the area under the flange. A point on the upper sheet is jointed to a tab to which an electrical lead is soldered. The bottom of the support is sweat soldered to a thin, circular metal sheet, the end of which at one point is jointed to a tab which extends past the top sheet and to which a second electrical lead is soldered. Upon loosening of a nut or bolt with which the invention is used, the spring forces the upper and lower elements apart until the hook shaped part contacts the flange of the support, thereby completing an electrical circuit between the two leads which signals the loose condition.

6 Claims, 2 Drawing Figures [52] U.S. Cl ..200/158, 85/62, ZOO/61.58 R [51] Int. Cl. ..H0lb 3/40 [58] Field of Search ..200/158, 83 N, 61.58 R, ZOO/51.14; 85/62, 61; 339/268, 259 R, 255 R [56] References Cited UNITED STATES PATENTS 2,713,102 7/1955 Lavarack et a1 ..200/158 2,822,530 2/1958 Roten ..200/83 N UX 3,233,059 2/1966 Pridham, Jr. et a1. ..200/83 N 3,046,369 7/1962 Hicks ..200/153 V UX 2,798,136 7/1957 Tarbox ..200/158 3,151,258 9/1964 Sonderegger et al. ..85/62 X 3,646,553 2/1972 Conkle ..85/62 X 3,495,907 2/1970 Rogers ..85/62 UX FOREIGN PATENTS OR APPLICATIONS 54,812 6/1923 Sweden ..85/62 09 L Iii 39 T ss 4| Patented May 29, 1973 3,736,394

INVENTOR DON K. RUMBAUGH CONDITION SENSING ASSEMBLY POSITIONED AS WASHER BACKGROUND OF THE INVENTION This invention relates generally to the fastener art, such as bolt fasteners and the like and, more particularly, relates to sensing devices installed with the fastening device to indicate the status thereof.

The importance of incorporating positive safety features in structures and constructions has been recognized. Mandatory installation of such devices in automobiles and other public conveyances has been proposed for critical steering, brake and suspension components.

In accordance with this invention, a device is provided which isinstalled much like a washer under nuts, bolt heads, and other fastening heads. The device produces a positive electrical signal directly in response to the loosening of the fastening device. The device is capable of sustaining the full load from bolts with which 2 it is used, and it may be completely moisture proof. In a preferred form, it is the same diameter and only slightly thicker than standard washers. No directly corresponding device is known in the prior art, since known devices similarly positioned measure strain and are not suited to producing a discrete warning signal upon loosening of a fastener.

The device according to this invention is installed with bolts, nuts and the like which, when loose or disconnected, could cause failure of operating parts, such as parts which could cause steering or brake failure. in an automobile, the device would close a circuit that turns on a warning light on the dashboard.

The device also has general burglar alarm applications. Anti-theft warning would be produced, for example, by the device installed with fasteners holding automobile stereo players, radios, spare tires and the like.

The device has wide usefulness for assuring safety and fail-safe operation in a large variety of public applications. For railroads, bolts would be monitored on undercarriage and car to car coupling, and in track switches. For airplanes, bolts would be monitored on engine mounts, nacelles, airframe attachments, control assemblies, hydraulic systems, landing gears and doors, helicopter rotor blades and controls. For rapid transit, monorail pylon attachment bolts and monorail support tower attachments would be monitored. Protection of users of both railroad and other bridges would be provided by monitoring of key bolts which have fairly high instance of loosening. The device would be used with ski lifts and tramways, and for military and space sys tems, in which fail-safe operation often is considered essential. Other applications of this invention in too large number to mention specifically will be immediately apparent since the device can be used to monitor fasteners without essential limitation as to the location or use of the fastener.

An important advantage of the device is that it is adapted to signal a danger condition when a fastener is merely loose, before it has failed substantially in function.

SUMMARY Accordingly, it is a primary object of this invention to provide an improved device to continuously monitor the condition of a fastener.

It is a more specific object of this invention to provide a practical and efficient sensing device to monitor the condition of a fastener.

It is another, more specific object of this invention to provide such a sensing device which is conveniently installed.

In accordance with this invention, two conductive members, each connected to a respective one of two leads in a status signaling circuit, are mounted for relative movement under the action of a spring member positioned between them. The conductive members are normally insulated from one another. One of the members has a part on the outside of the sensing device which extends toward the other member. The other member is formed and positioned so that the movement of the extending part is through a vacant area and then into contact with the other member to thereby close the signal circuit.

In the preferred embodiment, the device is circular 0 and largely symmetrical around a central hole provided to receive the shank or shaft of a nut, bolt or the like. The extending member hooks into and terminates under a flange in the other member. The body of other member from the flange to the hole is wide enough to provide resistance against undesired deformation under the forces applied by a tightened fastener. Both leads are connected to the members at positions on the outside of the device. insulation is provided by fiber layers. As the fastener becomes loosened prior to substantial failure of the fastener, the two conductive members contact to thereby close the signal circuit.

Further characteristics, objects, features and advantages of the invention will be apparent by reference to the following description of a preferred embodiment, as illustrated by the accompanying drawings.

BF DESC it!" '1 ON OF DRAWINGS FIG. 1 is a sectional view through the center of an installed device with the fastener tight and the signal circuit open.

FIG. 2 is the same as FIG. 1 except that the fastener is loose and the signal circuit is closed.

nus ON OF THE PREFERRED EMBODIMENT The drawings show the sensing device I presently preferred in accordance with this invention installed with a bolt 3. The head 5 of the bolt 3 contacts the top of the device I. The shaft 7 of the bolt 3 extends through a hole in the center of the device 1 and through plates 9 and 11, which, in FIG. 1, are held together tightly by bolt 3. Bolt 3 is shown threadingly engaged with plate ill, but, of course, that is merely illustrative, since various fasteners are equivalent, including, for ex ample, those threading on a nut at the end opposite the head of a bolt.

The sensing device, when assembled, is virtually entirely symmetrical in side cross section at all views through the center, as shown in FIGS. 1 and 2, except for tab 13 and tab 17. Tab 13 is a continuation of bottom conductive plate 15, which comprises a narrow extension terminated by a wider continuous circle adapted to receive a conductive lead. Tab 17, which is closely similar in form, is joined to the outside of upper conductive housing 19 above tab 13 by being silver brazed, spot welded or the like. Soldered connections 21 and 23 join two conductive leads 25 and 27 to the respective tabs 13 and 17. The device 1 may be stored and handled separately from the fastener 3 and need be brought into conjunction with the fastener 3 only when installed. The device itself is preferably entirely preassembled, but, of course, it may be assembled from individual elements during installation.

The device 1 comprises a top, heavy fiber lamination 29 providing electrical insulation, which is circular in plan, as are all the other elements with the exception previously mentioned regarding the electrical connections. Lamination 29 extends inward to a central hole provided for the shank of a fastener and, when installed, supports and insulates the nut or head of a fastener, as shown with respect to head 5 in F168. 1 and 2.

The upper conductive housing 19 is positioned under lamination 29 spaced a short distance from the central hole and extending outward from the center of the device l. Housing 19 has an outer portion which is bent to extend downward toward the bottom conductive plate 13 and then inward toward the center hole of the device 1. Tab 17 is jointed at one location to the downward extending part of housing 19.

A second heavy, fiber lamination 31 is positioned under the housing 119, where it extends outwardly from the center of the device. Element 31 also extends upward to fill the space between the hole in the device 1 and the start of area occupied by housing 19. When installed, element 31 supports upper housing 19 and insulates it from the lower members.

Located under element 31 is spring washer 33. This is a Belville washer, a round resilient steel element having a tendency to adopt a dish-like shape, as shown in cross section in FIG. 2. Spring 33 has a central hole to receive the shank of a fastener and rests upon conductive member 35, an integral, metal element comprising an upper flange defining the top of a vacant area into which the end of hook part of upper housing 19 extends. The width of the central hub of member 35 is sufi'icient to provide strength against collapse of the device 1 under the force of a tightened fastener.

Member 35 is extended electrically by bottom plate 15, upon which it is positioned and joined by sweat soldering. Bottom plate is circular and symmetrical except for the previously discussed extension, shown in the drawings, which provides a terminal connecting to electrical lead 25.

The metal members 15, 19 and 35 are preferably of stainless steel to provide resistance to rust in addition to adequate strength and electrical conductivity. A thin steel washer 37, positioned on top of fiber lamination 29 and having a central opening to receive shaft 7, extends to near the outside of the device, where it protects fiber lamination 29, particularly from abrasion by head 5. An 0 ring 39 of rubber or the like is bonded to the plate 15 in a full circle under the end of the hook of conductive housing 19, so as to provide a seal when the fastener is tight. A similar 0 ring 41 may be positioned under the device around the shaft 7 as shown to also provide a seal.

The drawings are generally illustrative of the relative In operation, the device 1 is provided separately and then installed on the shank of a fastener, such as shaft 7, under the head of the fastener. When the fastener is tight, as illustrated in FIG. 1, the spring 33 is collapsed, and the end of the hook of top conductor 19 is moved down into the vacant area defined by conductive element 35. The electrical signal circuit is open. The end of the hook of housing 19 tightly contacts ring 39 to seal out moisture and other possible agents of corrosion or other deterioration.

Should the fastener come loose or partially apart, spring 33 forces the upper conductor 19 and the fiber laminations 29 and 31 on the sides of it away from the lower conductive element 35. When the hook member contacts the flange of lower member 35, the signal circuit through plate 15 and leads 25 and 27 is completed. This completed circuit activates a warning, such as closing a power circuit through a warning light.

It will be apparent that the invention described may be implemented in difierent forms, some of which are immediately apparent and others of which may possibly include nonobvious aspects, but all of which would employ the substance of this invention. Accordingly, the patent coverage afforded this invention should not be limited essentially by the preferred embodiment described, but should be as provided by law, with particular reference to the accompanying claims.

What is claimed is:

1. A device for installation with a fastener comprising a first conductive member and a second conductive member normally electrically insulated from each other; said first conductive member having a part on the outer side of said device extending toward the second conductive member, said second conductive member defining an open area through which said extending part moves and then makes electrical contact with said second conductive member, an electric connector for making a signal circuit connected to said extending part of said first conductive member, a second electric connector for making said signal circuit connected to said second conductive member, on a part which is on the outer side of the device and a spring positioned between said first and second conductive members adapted to move them apart when not tightly held by a fastener, said device having a centrally positioned hole for receiving the shank of a fastener, said first conductive member having a flange on the side toward said spring with a vacant area at the side of said flange opposite said spring, said extending part extends past said flange and then back into said vacant area in the general form of a hook, said hook part being in said vacant area when said spring is collapsed while making electrical contact with said flange when said spring moves said members apart, a circular resilient ring positioned to be tightly contacted by said hook part when said first and second conductive members are held tightly by a fastener to seal the inside of said device from surrounding materials.

2. The device as in claim 1 in which a fiber layer adapted to provide electrical insulation is positioned on one side of said first conductive member and a second fiber layer adapted to provide electrical insulation is positioned on the other side of said first conductive member, said first conductive member being spaced from said central hole and normally supported and electrically insulated by said fiber layers.

3. The device as in claim 2 in which said second conductive member includes a part located between said flange and said hole which extends past said vacant area and is of sufiicient width to provide support to resist the forces of a tightened fastener.

4. The device as in claim 3 also comprising a lamination of abrasion-resistant material positioned on the outside of the outer of said fiber layers.

5. The device as in claim 3 in which said first conductive member, said fiber layers, said spring, said flange and said part located between said flange and said hole are all circular, symmetrical around said hole and substantially identical in cross section at all positions around said circle.

6. The device as in claim 5 in which one of said electioned on the outside of the outer of said fiber layers. i 

1. A device for installation with a fastener comprising a first conductive member and a second conductive member normally electrically insulated from each other; said first conductive member having a part on the outer side of said device extending toward the second conductive member, said second conductive member defining an open area through which said extending part moves and then makes electrical contact with said second conductive member, an electric connector for making a signal circuit connected to said extending part of said first conductive member, a second electric connector for making said signal circuit connected to said second conductive member, on a part which is on the outer side of the device and a spring positioned between said first and second conductive members adapted to move them apart when not tightly held by a fastener, said device having a centrally positioned hole for receiving the shank of a fastener, said first conductive member having a flange on the side toward said spring with a vacant area at the side of said flange opposite said spring, said extending part extends past said flange and then back into said vacant area in the general form of a hook, said hook part being in said vacant area when said spring is collapsed while making electrical contact with said flange when said spring moves said members apart, a circular resilient ring positioned to be tightly contacted by said hook part when said first and second conductive members are held tightly by a fastener to seal the inside of said device from surrounding materials.
 2. The device as in claim 1 in which a fiber layer adapted to provide electrical insulation is positioned on one side of said first conductive member and a second fiber layer adapted to provide electrical insulation is positioned on the other side of said first conductive member, said first conductive member being spaced from said central hole and normally supported and electrically insulated by said fiber layers.
 3. The device as in claim 2 in which said second conductive member includes a part located between said flange and said hole which extends past said vacant area and is of sufficient width to provide support to resist the forces of a tightened fastener.
 4. The device as in claim 3 also comprising a lamination of abrasion-resistant material positioned on the outside of the outer of said fiber layers.
 5. The device as in claim 3 in which said first conductive member, said fiber layers, said spring, said flange and said part located between said flange and said hole are all circular, symmetrical around said hole and substantially identical in cross section at all positions around said circle.
 6. The device as in claIm 5 in which one of said electric connectors is connected to the outside of said extending part and the other electric connector is connected to a part of said second conductive member which extends to the outside of said device past said extending part, and in which said device also comprises a circular, resilient ring positioned to be tightly contacted by said hook part when said first and second conductive members are held tightly by a fastener to seal the inside of said device from surrounding material and a lamination of abrasion-resistant material positioned on the outside of the outer of said fiber layers. 